Looking at my lighting earlier and see that my multimeter is measuring 230v from live to neutral at the ceiling light, but only70 ish volts from live to earth. Am I right in thinking the earth may be disconnected somewhere and the 70ish volts im reading is due to capacitance ? I cannot get my head round why its like this The live is definately at 230v so if the earth was disconnected I should not be getting any reading atall. Where is this 70v reading from ???? and between what ?? I need to check the continuity of the earth tomorrow but it cannot be continuous or i would be getting 230v, even a loose earth connection would still read full voltage would it not ??
But current flowing in capacitance is out of phase with the driving voltage, so does not represent any dissipation - you get back the electrons you put in to charge up the cables later in the cycle, (unused!).
This capacitive leakage is sometimes called the 'displacement' current, as it is the energy of setting up the electric field in the insulator, and then relaxing it again, like stretching and relaxing an ideal spring not actually doing any work in it - unlike a resistive leakage which would show at DC. (if you like images then a resistor is more like a frictional brake or well damped shock absorber, while a capacitance is more like an elastic, and to complete the picture an inductor is more like an inertial mass on low friction sliders, slow to get going and slow to stop but not much actual loss)
At least in principle you could tune out the capacitive reactance with an inductor of suitable value, and the have a circulating current oscillating back and forth between them but no net current driving current at all to speak of.
Of course this is not very practical (except perhaps on very long transmission lines of known geometry, where compensating reactors are indeed sometimes used,)
LV the network is slightly inductive anyway, so if anything stray capacitance helps a bit (indeed we add caps on motors and traditionally ballasted light fittings to try and keep amps and volts more or less together).
Of course the capacitance of cables is slightly lossy so the phase shift is not a perfect right angle, and there is some, but very little, actual dissipation.
But current flowing in capacitance is out of phase with the driving voltage, so does not represent any dissipation - you get back the electrons you put in to charge up the cables later in the cycle, (unused!).
This capacitive leakage is sometimes called the 'displacement' current, as it is the energy of setting up the electric field in the insulator, and then relaxing it again, like stretching and relaxing an ideal spring not actually doing any work in it - unlike a resistive leakage which would show at DC. (if you like images then a resistor is more like a frictional brake or well damped shock absorber, while a capacitance is more like an elastic, and to complete the picture an inductor is more like an inertial mass on low friction sliders, slow to get going and slow to stop but not much actual loss)
At least in principle you could tune out the capacitive reactance with an inductor of suitable value, and the have a circulating current oscillating back and forth between them but no net current driving current at all to speak of.
Of course this is not very practical (except perhaps on very long transmission lines of known geometry, where compensating reactors are indeed sometimes used,)
LV the network is slightly inductive anyway, so if anything stray capacitance helps a bit (indeed we add caps on motors and traditionally ballasted light fittings to try and keep amps and volts more or less together).
Of course the capacitance of cables is slightly lossy so the phase shift is not a perfect right angle, and there is some, but very little, actual dissipation.
